What is a HEPA air filter, anyway?

To facility managers, HEPA is a common phrase, but to the rest of the world it’s just a buzzword. The hype surrounding high-efficiency particulate arrestance (HEPA) filters is real, but how do these filters actually function? We have all the facts about air filtration for facility managers and indoor air quality enthusiasts alike.

Defining HEPA

High-efficiency particulate arrestance may sound like a loaded term, but essentially this designation is given to filters that use a combination of three methods to collect and remove dust and other contaminants from the air. In the U.S., HEPA standards created by the Department of Energy require filters to effectively remove 99.97 percent of dust particles 0.3 micrometers. If we move over the decimal point, it’s easy to visualize that these filters only allow about 3 of 10,000 particles to pass through.

HEPA terminology

Facility managers in particular should be wary of air purifier labeling, as some products use the term “HEPA-type filters,” which doesn’t require adhering to the U.S. standards. On the other hand, products labeled “PlasmaTrue™ and true HEPA filter technology,” such as the AeraMax® Professional, have been proven to meet these standards.

“Euro HEPA” is another term that gets thrown around often, but don’t let this designation fool you. Compared to U.S. standards, the European definition of a HEPA air filter is more lenient, mandating that the filter must only remove 85 percent of particles that are 0.3 micrometers.

How does a HEPA air filter work?

In the past, air purifiers with true HEPA filters have been used in buildings such as laboratories and health care facilities, but as continuing research reveals the health risks associated with poor IAQ, these devices can be more prevalent in shared spaces.

HEPA air filters don’t simply catch particles in the way you might imagine a fish getting caught in a net. Instead, these filters use air flow to catch particles by three different methods: impaction, interception and diffusion.

Impaction: Large particles in the airflow of a HEPA filter fly directly into one of the filter fibers and stick to it upon impact. These particles are big enough that the airflow pattern doesn’t push them around the fiber.

Interception: Medium-sized particles will somewhat follow the stream of air around each filter fiber, but they’ll veer off course slightly due to their inertia. The filter fibers then intercept these particles as they try and pass by.

Diffusion: The smallest particles bump into one another and behave more erratically, moving enough that it’s very unlikely they’ll get past a filter fiber without contact. Counterintuitively, this means that the smallest particles are not necessarily the hardest to filter.

In a true HEPA filter, these methods join forces to remove 99.97 percent of contaminants, including dust, allergens, germs and volatile organic compounds. Understanding this terminology makes it easier for facility managers to select the best air purifiers and proactively scrub IAQ problem areas.